A problem in the production of oil and gas from subsea wellbores is the undesirable formation of gas hydrates. A gas hydrate is a crystalline solid consisting of molecules of gas, usually methane, surrounded by a “cage” of water molecules. Gas hydrates have the visual appearance of ice. Methane hydrate is stable in ocean floor sediments at water depths of greater than about 300 meters. Certain temperature and pressure conditions encourage the formation of gas hydrates.
Gas hydrates pose a problem for the oil and gas industry as more deepwater gas enters the supply stream. Gas hydrates may form inside pipelines or in wellbores, slowing or completely blocking flow of hydrocarbons. Hydrate formation is a serious problem for producers moving gas from offshore wells to onshore processing facilities. Clearing plugged lines is expensive and time-consuming, and may take as long as twenty days. It has been estimated that controlling and preventing gas hydrate formation costs the industry hundreds of millions of dollars annually. It is very important to make changes or adjustments in wellbores to reduce the likelihood of gas hydrate formation.
In the production of oil and gas, it is sometimes necessary to employ downhole electrical submersible pumps to assist in moving oil from the formation to the surface in the wellbore. Submersible pumps are used in such operations to provide a relatively efficient form of “artificial lift”. By decreasing the pressure at the bottom of the well, more oil can be produced from the well when compared with natural production. Such pumps typically are electrically powered and may be referred to as Electrical Submersible Pumps (“ESP”).
ESP systems may be subject to undesirable cavitation if excess gas is present in the flow stream being pumped. Shock waves caused by cavitation in pumps may damage moving parts within the pump. It is desirable to avoid entrained gas in production fluids that are to be pumped by a downhole ESP to avoid damage to pumps.